1. Field for the Invention
The present invention relates generally to the manufacture of circuit board assemblies, and more particularly to a multilayer circuit board assembly and a method for generating tool masters therefor.
The development of printed circuits has provided many advantages over previous techniques, including reliability, reduction of cost, and reproducibility of circuits. The multilayer printed circuit board further extended the capabilities of the art by allowing greater density of interconnections, shorter circuit runs, and conservation of space.
2. Description of the Prior Art
The methods of designing multilayer printed-circuit boards in the prior art are characterized by extended design time, long lead time for fabrication and high cost, especially for short production runs. This is due to the multiplicity of steps involved in generating coordinated artwork for a plurality of circuit layers. Each step must maintain a high degree of accuracy and tolerances for each individual circuit layer in order to achieve the overall accuracy required for the assembled board. Multilayer board artwork is generally custom-designed for only one printed-circuit board type. Such custom designs are difficult to modify and virtually impossible to repair without special facilities.
One prior art method of multilayer board design which succeeded in alleviating some of the above-mentioned problems utilized preconfigured internal circuit layers having a plurality of multiterminal circuit paths crossing the board, and uniquely designed outer circuit layers interconnected via the internally disposed crossboard circuits. This prior art method confined circuit routing largely to the internally disposed layers and constrained circuit design by producing internally disposed circuit stubs of substantial length which were potentially degrading to the operation of certain circuits.